Feasibility of Pb
1-x Sn
x Te diode lasers to a high resolution spectroscopy was examined. The laser diode was cooled by liquid helium. Laser emission frequencies were tuned by varying the diode current. A threshold current for cw oscillation by liquid helium cooling was one third or less of that by liquid nitrogen cooling. The lasers oscillated in a few longitudinal modes simultaneously, so a 25cm grating monochromator was used as a mode selection filter. The laser emission from 580cm
-1 to 1450cm
-1 was obtained by changing x=0.14-0.22. Some absorption spectra of NH
3, SF
6 and CF
4, and a gain spectrum of a cw CO
2 laser was observed. Spectral resolution of the experimental equipment was 8×10
-4cm
-1, and it was confirmed that the resolution is mainly limited by the diode driving current.
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